The present invention relates to a brake system having primary and secondary brakes.
Certain jurisdictions, such as Europe, have regulations which require off road vehicles, such as tractors, both primary and secondary brake systems to help stop the vehicle when the vehicle is traveling at a high speed. For example, all tractors sold in Europe are required to have primary service brakes which operate in the rear axle and which are controlled by independent foot pedals. Typically, the foot pedals operate a brake valve which transmits pressurized fluid to brake pistons which clamp the brake disk between the piston and a reaction plate. A secondary brake system is normally located in the front axle and is actuated by a hand lever. The secondary brake system also includes a piston which clamps a brake rotor against a stationary reaction plate.
Especially at high speeds, such a secondary brake system will create frictional drag and power loss, even when the secondary brake is not being applied. Also, such a secondary brake system takes up limited space in the front axle assembly, and it is difficult to include in a front axle assembly a secondary brake which is large enough to handle the heat generated by application of the secondary brake.